Hilea_Final_Hydraulics_Report.pdf

III

Contents Section Page

1 Introduction ............................................................................................................................... 1-1

1.1 General ................................................................................................................................... 1-1

1.2 Project Location and Identification ........................................................................................ 1-1

2 Existing Site Conditions ............................................................................................................... 2-1

2.1 General ................................................................................................................................... 2-1

2.2 Bridge ..................................................................................................................................... 2-1

2.3 Hilea Stream ........................................................................................................................... 2-1

2.4 Culverts .................................................................................................................................. 2-1

2.5 Roadside Ditches .................................................................................................................... 2-1

2.6 Floodplain .............................................................................................................................. 2-1

2.7 Wetlands ................................................................................................................................ 2-2

2.8 Water Quality ......................................................................................................................... 2-2

3 Design Criteria and Methodology ............................................................................................... 3-1

3.1 Applicable Drainage Criteria .................................................................................................. 3-1

3.2 General Design Criteria .......................................................................................................... 3-1

3.3 Hydrologic Design .................................................................................................................. 3-1

3.4 Hydraulic Analysis .................................................................................................................. 3-2

3.5 Criteria for Temporary Drainage Facilities ............................................................................. 3-2

3.6 Other Criteria and Methodology ........................................................................................... 3-3

3.7 Fish Passage ........................................................................................................................... 3-3

4 Hydrologic and Hydraulic Analyses ............................................................................................. 4-1

4.1 Hydrologic Analysis ................................................................................................................ 4-1

4.1.1 General...................................................................................................................... 4-1

4.1.2 USDA SCS 1988 Report.............................................................................................. 4-1

4.1.3 Precipitation Data ..................................................................................................... 4-1

4.1.4 Hydrology for Roadway Drainage ............................................................................. 4-1

4.2 Hydraulic Analysis .................................................................................................................. 4-2

4.2.1 Existing Bridge ........................................................................................................... 4-2

4.2.2 Proposed Bridge ........................................................................................................ 4-2

4.2.3 Surface Drainage ....................................................................................................... 4-2

4.2.4 Bridge Scour .............................................................................................................. 4-2

4.2.4.1 Site Geology .............................................................................................. 4-2

4.2.4.2 Scour Design Flows ................................................................................... 4-3

4.2.4.3 Scour Parameters ..................................................................................... 4-3

4.2.4.4 Stream Degradation ................................................................................. 4-3

4.2.4.5 Contraction Scour ..................................................................................... 4-4

4.2.4.6 Pier Scour .................................................................................................. 4-4

4.2.4.7 Abutment Scour ........................................................................................ 4-5

4.2.4.8 Scour Results ............................................................................................ 4-5

5 Summary .................................................................................................................................... 5-1

6 References .................................................................................................................................. 6-1

CONTENTS

IV

Appendices

A Hydrology B Hydraulics C Scour Analysis D Photographs E HDS Addendum

Tables

4-1 Hydrologic Flows .................................................................................................................................. 4-1

4-2 Sediment Regime Parameters – 100 Year Event ................................................................................. 4-4

4-3 Contraction Scour Parameters – 100 Year Event ................................................................................. 4-4

4-4 Froehlich/HIRE Abutment Scour Parameters - 100 Year Event (Manual Calculation) ......................... 4-5

4-5 NCHRP 24-20 Abutment Scour Parameters – 100 Year Event ............................................................. 4-5

4-6 Summary of Hilea Stream Scour Depth Results ................................................................................... 4-6

Figures

1-1 Vicinity Map (Google earth) ................................................................................................................. 1-1

4-1 Hilea Stream Bridge 50-year Water Surface Profiles ........................................................................... 4-3

4-2 Scour Depth Profile from NCHRP Method ........................................................................................... 4-6

SECTION 1

1-1

Introduction

1.1 General

Central Federal Lands Highway Division (CFLHD) is working with the Hawaii Department of Transportation (HDOT) to provide bridge replacements for multiple bridges throughout the Hawaiian Islands. This report presents the results of a site reconnaissance and final drainage analyses performed at the Hilea Bridge site on the southern side of the Hawaii Island in the state of Hawaii. The report includes a final hydraulics design and analysis for the replacement of the existing deficient timber bridge.

1.2 Project Location and Identification

The Hilea Bridge spans the Hilea Stream at MP 57.72 along the Hawaii Belt Road (Mamalahoa Highway/ Route 11) on the Island of Hawaii in the state of Hawaii. The bridge is located approximately 5.6 miles northeast of the Town of Naalehu in Hawaii County. Based on the North American Datum of 1983 (NAD83), Hilea Stream Bridge is located at 19° 7'28.85"N latitude and 155°31'33.32"W longitude. See Figure 1-1 for Vicinity Map (Reference 1).

FIGURE 1-1

Vicinity Map (Google earth)

SECTION 2

2-1

Existing Site Conditions

2.1 General

A site investigation of the Hilea Bridge was conducted on January 14, 2014 by CH2M, CFLHD, HDOT ParEn (Hydraulics), Hirata (Geotech), and KSF (Structures). The bridge is located on Mamalahoa Highway, Routh 11, which is a two-lane asphalt paved road with 10-foot lanes and 2-3 foot shoulders. The roadway is maintained by HDOT and is located in the HDOT right-of-way (ROW). The roadway is generally crowned and runoff sheet flows off of the pavement to roadside ditches.

2.2 Bridge

The existing bridge was built in 1940. It consists of a 2-span, 40-foot long structure supported by a timber pier on a stone and concrete foundation. It is supported at each end by vertical-walled concrete abutments.

The existing bridge is inadequate to convey the 50-year design flow as calculated from the TR-20 method in the published 1988 USDA SCS Report (Reference 2) and the roadway is frequently overtopped. The existing bridge is overtopped with a 50-year water surface elevation at 148.85 feet. About 200 yards upstream of the bridge, the water exceeds bank-full capacity and spreads out into the overbanks as it approaches the Hawaii Belt Road. There is a wooden slat guard rail on each side of the road over the bridge. The rail collects debris and blocks flows when the roadway overtops according to HDOT maintenance.

See Appendix D for existing bridge photos.

2.3 Hilea Stream

Hilea stream is an intermittent stream that drains approximately 31.3 square miles of the southern slope of Mauna Loa. Due to the highly permeable nature of fissures in the lava flow in this basin, only 11.06 square miles of the Hilea basin is used for hydrology study as per the 1988 USDA SCS Report. Discussions with HDOT confirmed the hydrologic approach of eliminating the higher elevation areas from contributing direct runoff to the bridge. Field observations indicate that the stream is located in rock. Rock outcrops were observed around and under the bridge. Gravel cobbles and boulders were also observed at various locations within the channel. There were approximately three (3) existing knick-points (natural drops) observed downstream of the existing bridge. The knick points were approximately 2 feet to 3 feet in height. Channel overbanks are heavily vegetated.

2.4 Culverts

There are no culverts within the project limits.

2.5 Roadside Ditches

For existing conditions, runoff from the highway sheet flows off of the road into roadside ditches. The ditches run along rock embankments, are partially vegetated, and drain towards Hilea Stream. For proposed conditions, runoff will be conveyed in the same manner.

2.6 Floodplain

The Hilea Bridge is not located within a FEMA-regulated floodplain, according to the FEMA Flood Insurance Rate Map, Community Panel No. 1551661695C dated September 16, 1988. The project is located within Zone X of the special Flood Hazard Area.

2 EXISTING SITE CONDITIONS

2-2

2.7 Wetlands

No wetlands exist within the survey area of the Hilea Stream as per the “Ordinary High Water Mark (OHWM) delineation in Hilea Gulch and Ninole Gulch, Kau District, Hawaii” report (Reference 3). This report is waiting the final confirmation that there are no wetlands from USACE.

2.8 Water Quality

No permanent storm water quality facilities are required for this site. Appropriate temporary erosion and sediment control BMPs will be required during construction.

SECTION 3

3-1

Design Criteria and Methodology

3.1 Applicable Drainage Criteria

Criteria and methods will be consistent with the HDOT Highways Division “Design Criteria for Highway Drainage,” dated October 2010, as amended (Reference 4). For criteria and guidance not included in the HDOT manual, the guidance in the Federal Lands’ Project Development and Design Manual (PDDM) Chapter 7 (Reference 5) will be followed. The following sections are excerpts from the HDOT Manual, using only information that is applicable to the Hilea Bridge replacement project. The last section, Other Criteria and Methodology, outlines applicable guidelines and criteria not found in the HDOT manual.

3.2 General Design Criteria

The following are general guidelines and policies for highway design projects.

• Capacity of proposed facilities shall not be less than the capacity of the existing facilities

• The proposed design shall take into consideration the accessibility of maintenance personnel to inspect and clean the facilities.

• Utilities and conduits shall not be installed inside of the proposed drainage facilities.

3.3 Hydrologic Design

Hilea Bridge is located along Mamalahoa Highway, Route 11 near Mile Post 57.7. Mamalahoa Highway is functionally classified as a rural minor arterial roadway. The highway is not on the National Highway System.

As such, the design recurrence interval selected in the analysis of existing and proposed drainage facilities shall be in accordance with the following:

Recurrence Intervals (yrs)

Functional Classification

Bridge/Culvert Crossing

Roadway (at grade)

Roadway (sump)

Arterial 50 25 25

The project site is not located within a mapped Federal Emergency Management Agency floodplain.

Therefore, the design of the replacement bridge is not required to comply with the National Flood Insurance Program’s regulations and requirements.

• The bridge shall be analyzed for the 50-year storm event.

• Ditches and channels designed to intercept and divert runoff from off-site shall be based on a recurrence interval used for roadway crossings.

• For recurrence intervals used to determine scour potential at bridges, refer to applicable FHWA Hydraulic Engineering Circulars and HDOT Highway Division manual, “Design Criteria for Highway Drainage.”

• Point rainfall values shall be interpolated from the National Oceanic and Atmospheric Administration’s (NOAA) Precipitation Frequency Data Server website:

http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_map_hi.html.

3 DESIGN CRITERIA AND METHODOLOGY

3-2

The following hydrologic methods are selected to determine peak discharge for this project. Refer to the Hilea Hydraulics Recommendations Report (Reference 6) for a description of other hydrologic methods analyzed.

Rational Method (as needed for roadway runoff analysis) – The Rational Method shall be used to estimate peak flow rates for drainage areas up to 200 acres. This method is applicable at small culvert crossings, and can be exclusively used for on-site roadway drainage. The minimum time of concentration shall be 10 minutes.

USDA SCS 1988 Report – The peak discharges from this report are used for hydrology analyses in this project. The peak discharges are calculated using the TR-20 method.

The 5- year peak discharge found in the 1988 Report shall be included in this hydraulics report for consideration by the Contractor during their design of temporary drainage facilities.

3.4 Hydraulic Analysis

Bridge Crossings

• Bridges shall be designed with a minimum freeboard of two feet. Freeboard shall be defined as the vertical distance between the approach design water surface elevation and the low chord of the bridge.

(A variance or design exception may be required due to the vertical profile of the roadway and the surrounding topography.)

• Bridge abutment face shall be set back from the main stream channel section to minimize potential abutment scour. Design smooth transition from the abutment to the upstream channel embankment.

• Bridge scour shall be designed for the 100-year recurrence interval.

• The minimum cross-slope of the bridge deck shall be 1.5%.

• The minimum longitudinal slope along the bridge deck shall be 0.5%. Longitudinal slopes less than the minimum may be accepted in areas restricted by physical parameters.

• Runoff discharge directly into the stream channel shall be minimized.

• Attention is directed to Appendix C on memorandum HWY-DH 2.2443, “Invert Lining at Highway Bridges,” dated 6/26/09. The memorandum describes lining of bridge invert as a possible scour protection measure.

• Water surface elevations and peak flow rates for the 50- and 100-year storm events shall be shown in the Contract Plans.

Roadside Gutters and Ditches

• Maximum cross-slope within the highway clear zone shall be 6:1. Preferred cross-slope within the clear zone is 12:1.

• The backslope of V-shaped gutters in cut sections shall be no greater than the slope of the cut-section.

3.5 Criteria for Temporary Drainage Facilities

The Contractor shall provide the drainage design of temporary construction-related drainage facilities, including roadway detours. Design, layout and construction of the detour road, including erosion and sediment control BMPs, shall be performed by the Contractor. HDOT criteria states, “The recurrence interval for detour road crossings shall be equivalent to a five year storm event.” See Appendix B section of HDOT’s Design Criteria for Highway Drainage Manual for further guidelines for the design of temporary drainage facilities. Temporary channel diversions not associated with the roadway diversion shall be designed to convey, at a minimum, the five-year storm.

3 DESIGN CRITERIA AND METHODOLOGY

3-3

3.6 Other Criteria and Methodology

• Bridge deck drainage design shall follow the guidance of HEC-21 Design of Bridge Deck Drainage

(Reference 7).

• Section 7.3.3.5 Bridge Deck Design Guidance of the PDDM shall be considered in the bridge design.

• Section 7.4.2.4.4 Bridge Scour of the PDDM shall be considered when designing for debris at piers.

• Section 7.4.3.4.1 Capacity Design of the PDDM shall be considered for freeboard when the potential for woody debris is significant.

In addition to the above criteria, applicable sections of the attached HDS Addendum to Design Flood Criteria updated April 16, 2015 shall apply to this project. See attachment in Appendix E.

3.7 Fish Passage

There are no requirements for fish passage design for this project. Any encroachment into the Hilea Stream for pier removal or construction of bank stabilization improvements will be on a temporary basis and the channel geometry below the normal flow of the river will be restored to its original configuration.

SECTION 4

4-1

Hydrologic and Hydraulic Analyses

4.1 Hydrologic Analysis

4.1.1 General

Multiple methods were employed to analyze the hydrology for the Hilea Bridge drainage basin including USGS StreamStats, USGS Regional Regression Equations, Regression Equations used by FEMA in the Hawaii County FIS for similar nearby drainage basins and USDA SCS 1988 Report. The drainage area of 31.3 square miles exceeded the recommended 25 square-mile limit used by TR-55 (Reference 8), so TR-55 was not used for comparison. Details of each method are described in the Hydraulics Recommendation Report for the Hilea Bridge Replacement by CH2M dated March 2015. A description of the selected hydrologic method is included below.

4.1.2 USDA SCS 1988 Report

A Hilea Stream Preliminary Engineering Report by the United States Department of Agriculture Soil Conservation Service, dated August 3, 1988, provided results of a TR-20 hydrologic analysis for the Hilea Bridge on Route 11. The 1988 report based its results on a drainage basin area of 11.06 square miles, excluding the contributing drainage basin above elevation 6,000 feet due to the highly permeable nature of fissures in the lava flow, which eliminate surface runoff to the lower elevations. The hydrology from this report was used for this project. The published USDA SCS 1988 results for the 50-year runoff appeared the most reasonable for the design flow based on the following reasons:

• Surface flows above 6,000 ft on which other equations are based upon would not reach the Hilea Bridge due to the highly permeable nature of fissures in the lava flow.

• TR-20 is a methodology acceptable to HDOT and CFLHD.

Below is a table of the hydrologic flows for the Hilea Stream at the Hilea Bridge as documented in the USDA SCS 1988 Report.

TABLE 4-1

Hydrologic Flows

Flow (cfs) at Hilea Bridge

Storm Frequencies (based upon drainage area of approximately 11.1 mi²)

Q(2) Q(5) Q(10) Q(25) Q(50) Q(100)

1,350 * 3,000 * 4,300 * 6,500 * 8,100 * 10,650 *

* Assuming no contributing runoff from above 6,000 feet.

See Appendix A for excerpts from the 1988 report.

4.1.3 Precipitation Data

Precipitation values for the 2-year through 100-year storms, for durations for 5-minutes through 24 hours, were obtained from the NOAA Atlas 14 website for Hawaii (Reference 9). See Appendix A for rainfall data.

4.1.4 Hydrology for Roadway Drainage

No analysis was performed for surface roadway flows at the bridge as beam and post rail will be used with no curbs or inlets to collect or convey runoff. Runoff will sheet flow off of the bridge directly to the channel below.

4 HYDROLOGIC AND HYDRAULIC ANALYSES

4-2

There are no defined ditches for the existing roadway cross section, which is cut into a lava flow. Rain falling onto the lava flow area will be captured in depressions and dissipated in fissures. Although V-ditches were included in the proposed roadway cross section in the vicinity of the bridge, no hydrology was performed for the sizing of these ditches.

4.2 Hydraulic Analysis

4.2.1 Existing Bridge

The existing bridge is approximately 40 feet long with two spans and a low-chord-to-invert clearance of approximately 12 feet. Survey data was obtained for the Hilea stream and bridge and was used to develop cross sections for hydraulic modeling in HEC-RAS. Preliminary modeling results indicate that the existing bridge with a 40- foot opening is being overtopped by the 50-year peak flow of the USDA SCS 1988 Report (8,100 cfs). See Appendix B for the HEC RAS model output for existing condition.

4.2.2 Proposed Bridge

The proposed bridge replaces the existing structure with a total new bridge length of 106 feet and a width of 42’-4” including 1’-2” railing width on both sides. The bridge opening length is 100 feet. The new bridge will be a single span bridge using 3 feet deep precast girders. The proposed bridge will have a 2’-8” high concrete post and beam bridge rail capped with a 10-inch high metal railing for a total height of 3’-6” for bicyclist safety at both ends. The existing abutments and pier will be removed and grading will need to take place to transition from the existing channel to the new bridge abutments. The proposed southwest abutment will be placed at approximately 54 feet behind the existing abutment and the proposed northeast abutment will be placed at approximately 6 feet behind the existing abutment. The proposed abutments will be socketed into the intact rock. The proposed wingwalls are oriented at 90 degrees with the proposed abutments at both ends of the bridge. Construction work will be allowed to take place within the ordinary high water mark of the stream. The bridge is sized to convey the 50-year peak flow of 8,100 cfs, even though a split flow occurs upstream of the bridge. There have been published documents, including the 1988 USDA SCS Report, regarding upstream improvements to the channel embankments to eliminate the split flow (by others);

therefore the bridge was sized assuming improvements would occur in the future. See Appendix B for the HEC RAS model output for the proposed condition.

See Figure 4-1 for the 50-year water surface profile comparison between the existing and proposed conditions.

4.2.3 Surface Drainage

Surface runoff from roadway will be conveyed through proposed ditches in the cut area before daylighting.

In the fill area, runoff will sheet flow off the embankment. No ditches were analyzed for this project. Beam and post rails will be used along the bridge, so runoff will sheet flow off of the bridge and discharge directly into the channel below. Rolled erosion control product (RECP), Type 4 is recommended to use along embankment slopes steeper than 1V:3H unless the ditches are cut into rock.

4.2.4 Bridge Scour

4.2.4.1 Site Geology

The borings performed by Hirata & Associates, Inc., (Reference 11) at the northeast and southwest bridge abutments consists of grayish brown well-graded gravel mixed with silt, basaltic sand, and cobbles.

4-3

FIGURE 4-1

Hilea Stream Bridge 50-year Water Surface Profiles

The granular soils extends to depths of about 15 and 11.5 feet at the northeast and southwest abutments respectively. Below the granular material, gray, slightly weathered basalt in hard condition exists, extending to the maximum depths drilled. Neither groundwater nor seepage was encountered in the borings. The proposed Hilea bridge will have shallow foundations embedded/socketed into hard basalt to a minimum depth of 5 feet and bridge stability due to scour will not be a concern. The scour data shown in this report assumes granular material to determine the scour depths and is included in this report for information only.

4.2.4.2 Scour Design Flows

The Q100 of 10,650 cfs is used as the maximum scour flood.

4.2.4.3 Scour Parameters

As recommended by HEC-18 (Reference 12), long-term stream degradation, contraction scour, and abutment scour were assessed for the bridge. The median bed material size (D50) for the subsurface material was determined to range between 2.3 mm and 8.1 mm taken from the gradation curves at borings HL1 and HL2 from the geotechnical report. The left abutment and right abutment from HEC-RAS model mentioned in this report refers to the Abutment No. 1 and Abutment No. 2 respectively on the plan sheet. The following sections describe the development of the equation parameters for each type of scour.

4.2.4.4 Stream Degradation

By comparing the existing Hilea bridge low chord to channel thalweg clearance between the as-builts dated Nov. 1938 and the current survey data dated Oct. 2014, it was found that the Hilea Stream has degraded by approximately 3.8 feet. As-builts show the clearance of 11.6 feet and the current survey data shows the

4-4 clearance of 15.4 feet along the centerline of the Hilea Bridge. Based on established vegetation and rock in the channel invert of the bridge, it is estimated that no further degradation will occur. See Appendix C for as built drawing of existing Hilea bridge.

4.2.4.5 Contraction Scour

The parameters used in the contraction scour equations were determined from proposed Hilea HEC-RAS model and by running the 100 -year flood event through the model. Section 624.6436, which is located approximately 24 feet upstream from the Hilea Bridge, was chosen as the approach cross-section. This section accurately represents the general channel geometry upstream from the bridge, and it was compared to the contracted bridge cross-section to determine the magnitude of the contraction scour.

Based on average velocity (V) and critical velocity (Vc) calculations in the approach cross-section, the live-bed contraction scour equation was used for the main channel and left and right abutments. Table 4-2 shows the parameters used to calculate the sediment regime in the channel and the left and right abutments.

TABLE 4-2

Sediment Regime Parameters – 100 Year Event

Parameters Left Overbank Channel Right Overbank Unit

Ku 11.17 11.17 11.17 y 2.51 7.09 2.7 ft

D50 0.008 0.008 0.008 ft

V 3.26 10.78 3.42 ft/s

Vc 2.60 3.10 2.64 ft/s

Sediment Regime Live-bed Live-bed Live-bed

The width for the approach cross section was defined as the bottom width of the channel that is transporting bed material. For the contracted bridge cross-section, the total bottom deck width was used for the channel width less pier widths. These widths are intended to reflect the portions of the channel which are actively mobilizing sediment. The flow area and channel flows were determined from the flow distribution within the channel widths. Table 4-3 summarizes the parameters used to calculate the contraction scour for the Hilea Bridge. Variables with a subscript of 1 and 0 indicate the stream approach cross-section at section 624.6436 and variables with a subscript of 2 indicate the contracted bridge cross-section at section 575 BR U. Complete scour calculations are presented in Appendix C.

TABLE 4-3

Contraction Scour Parameters – 100 Year Event

Parameters Left Overbank Channel Right Overbank Unit y1 2.51 7.09 2.70 ft yo 10.10 ft

Q2 10,650 ft3/s

Q1 518.64 7454.12 2677.24 ft3/s

W1 63.36 97.61 290.38 ft

W2 0 100 0 ft

K1 0.69 0.69 0.69 y2 0 9.47 0 ft ys (scour depth) 0 ft

4.2.4.6 Pier Scour

There are no piers to analyze for the proposed single-span Hilea Bridge.

4-5

4.2.4.7 Abutment Scour

As recommended in HEC-18, Froehlich, HIRE, and NCHRP 24-20 scour equation methods were all computed to calculate abutment scour depths of the proposed Hilea Bridge. A summary of each methodology is described below.

Froehlich/HIRE Abutment Scour Methods. The abutment scour depths using Froehlich/HIRE methods were computed manually using the output results from HEC-RAS run for 100-year event. Table 4-4 shows the parameters used to calculate the abutment scour depth using Froehlich/HIRE methods for the 100-year event manually.

TABLE 4-4

Froehlich/HIRE Abutment Scour Parameters - 100 Year Event (Manual Calculation)

Parameters Left abutment Right abutment Unit

Qe 423.8 188.10 ft3/s

Ae 130 55.00 ft²

Ve 3.26 3.42 ft/s

L' 41 15 ft ya 3.17 3.67 ft

L'/ya 12.93 4.09

Fr 0.32 0.31

K1 1 1

K2 (ϴ=90°) 1 1

Equation Froehlich Froehlich ys (scour depth) 14.02 11.20 ft

NCHRP 24-20 Method. NCHRP 24-20 is another method to calculate the abutment scour depth. It calculates the total scour at the abutments including contraction scour, so no separate contraction scour is calculated. For the Hilea Bridge, the left and right abutments were projected to upstream Section

624.6436 of the HEC-RAS model to calculate the projected length of the left and right embankments.

Table 4-5 shows the parameters used to calculate the abutment scour depth using the NCHRP method for the 100-year event. Parameters with a subscript of 1 indicate the stream approach cross-section at section 624.6436 and variables with a subscript of 0 and 2 indicate the contracted bridge cross-section at section 575 BR U. Complete scour calculations are presented in Appendix C.

TABLE 4-5

NCHRP 24-20 Abutment Scour Parameters – 100 Year Event

Parameters Main channel hydraulics Unit y1 7.09 ft q2c 106.50 ft²/s q1 76.37 ft²/s yc 9.43 ft αA 1.72 ymax 16.22 ft yo 10.10 ft ys (scour depth) 6.12 ft

4.2.4.8 Scour Results

The results of the scour analysis are summarized in Table 4-6. While comparing the abutment scour depth results from the NCHRP 24-20 method with the Froehlich/HIRE method, Froehlich/HIRE results were found

4-6 to be too conservative due to the sensitivity of the parameters and coefficients used in the equations and therefore, NCHRP 24-20 method was recommended to design the proposed abutment scour depth.

Figure 4-2 presents the theoretical scour depths from a profile view of the bridge using the NCHRP 24-20 method. Detailed scour calculations are located in Appendix C.

TABLE 4-6

Summary of Hilea Stream Scour Depth Results

Methods Left abutment Channel Right abutment Unit

Long-Term Degradation 0 ft

NCHRP 24-20 method 6.12 6.12 ft

Total local scour depth 6.12 6.12 ft

Manual calculation

Contraction scour 0 ft

Froehlich/HIRE method 14.02 (Froehlich) 11.20 (Froehlich) ft

Total local scour depth 14.02 11.20 ft

FIGURE 4-2

Scour Depth Profile from NCHRP Method

SECTION 5

5-1

Summary The need for a larger bridge opening at the Hilea stream crossing is apparent due to the frequency of overtopping at this location. Peak discharges from the USDA SCS 1988 Report were selected to determine the capacity of the proposed bridge. The existing bridge overtops with a 10-year runoff of 4,300 cfs. In order for the proposed bridge to convey the 50-year flow of 8,100 cfs with a two-foot freeboard and no roadway raise, a wider bridge opening is required. A 106-foot bridge length with a hydraulic opening of 100 feet would meet the conveyance and freeboard requirements. The proposed bridge will be a single span structure. Note that although the 2-foot freeboard is achieved at the upstream face of the bridge, the water surface elevation jumps to the low chord elevation at the next upstream cross section. Also note that although the proposed bridge is sized to convey the full 50-year runoff from the drainage basin, split flow conditions would still occur upstream, allowing flow to break away from the channel and overtop the road just northeast of the bridge.

A HEC-RAS (Reference 13) analysis was performed, incorporating backwater calculations and bridge losses, to provide an accurate hydraulic model to determine the proposed bridge dimensions. However, the scour depth computation from Froehlich/HIRE equations are conservative, so the NCHRP 24-20 method is used to calculate the abutment scour depth for the 100-year event. The scour data shown in this report is for information only since the bridge abutments are socketed into basalt.

Temporary erosion and sediment control BMPS shall be used in accordance with CFLHD standards and FP-14 specifications (Reference 14).

SECTION 6

6-1

References

1. “Hilea Bridge.” 19° 7'28.85"N and 155°31'33.32"W. Google Earth. April 9, 2013. November 1, 2014.

2. USDA SCS Hilea Stream Preliminary Engineering Report, August 3, 1988.

3. Ordinary High Water Mark (OHWM) delineation in Hilea Gulch and Ninole Gulch, Kau District, Hawaii, prepared by AECOS, Inc. January 9, 2015, Revised March 20, 2015.

4. State of Hawaii Department of Transportation Highways Division Design Criteria for Highway Drainage 10/1/10.

5. Federal Highway Administration, 2011. “Federal Lands Highway Project Development and Design Manual”, U.S. Department of Transportation, Washington, DC

6. “Hydraulics Recommendations Report, Hilea Bridge Replacement, Mamalahoa Highway, Route 11, District of Kau, Island of Hawaii, State of Hawaii”, prepared for Federal Highway Administration, Central Federal Lands Highway Division by CH2M HILL, March 2015.

7. HEC-21, “Design of Bridge Deck Drainage”, Hydraulic Engineering Circular No. 21, FHWA-SA-92-010, 1993.

8. Technical Release 55 (TR-55), 1986, “Urban Hydrology for Small Watersheds”

9. NOAA ATLAS 14 Volume 4 Precipitation Frequency Data Server (PFDS) http://www.nws.noaa.gov/oh/hdsc/index.html/

10. HEC-23, “Bridge Scour and Stream Instability Countermeasures: Experience, Selection, and Design Guidance”, FHWA-NHI-09-111, 2009, Volume 1 and 2, Third Edition

11. Interim Geotechnical Memorandum, prepared for CH2M HILL, February 13, 2015 by Hirata & Associates, Inc.

12. HEC-18, “Evaluating Scour at Bridges”, Hydraulic Engineering Circular No. 18, FHWA-HIF-12-003, April 2012, Fifth Edition.

13. U.S. Army Corps of Engineers, 2010, "HEC-RAS, Hydrologic Engineering Centers River Analysis System,” Version 4.1

14. Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects, FP-14

15. Federal Highway Administration (FHWA-NHI-02-001), 2002. “Highway Hydrology”, Hydraulic Design Series No. 2, U.S. Department of Transportation, Washington, DC, Second Edition.

16. StreamStats (USGS) http://water.usgs.gov/osw/streamstats/ssonline.html/

17. Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture.

Web Soil Survey. Available online at http://websoilsurvey.nrcs.usda.gov/. Accessed [10/20/2014].

18. Federal Emergency Management Agency. Flood Insurance Study: Hawaii County, Hawaii, April 2, 2004.

Appendix A Hydrology

Soil Report

Soil Map—Island of Hawaii Area, Hawaii (Hilea_Soil Report)

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

11/13/2014

233700 233900 234100 234300 234500 234700 234900

233700 233900 234100 234300 234500 234700 234900

19° 7' 58'' N

5°

1'

4' ' W

19° 7' 58'' N

5°

1'

1'

' W

19° 7' 4'' N

5°

1'

4'

' W

19° 7' 4'' N

5°

1'

1'

' W

N

Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 5N WGS84 0 350 700 1400 2100

Feet 0 100 200 400 600

Meters Map Scale: 1:8,220 if printed on A portrait (8.5" x 11") sheet.

MAP LEGEND MAP INFORMATION

Area of Interest (AOI) Area of Interest (AOI)

Soils Soil Map Unit Polygons

Soil Map Unit Lines

Soil Map Unit Points

Special Point Features Blowout

Borrow Pit

Clay Spot

Closed Depression

Gravel Pit

Gravelly Spot

Landfill

Lava Flow

Marsh or swamp

Mine or Quarry

Miscellaneous Water

Perennial Water

Rock Outcrop

Saline Spot

Sandy Spot

Severely Eroded Spot

Sinkhole

Slide or Slip

Sodic Spot

Spoil Area

Stony Spot

Very Stony Spot

Wet Spot

Other

Special Line Features

Water Features Streams and Canals

Transportation Rails

Interstate Highways

US Routes

Major Roads

Local Roads

Background Aerial Photography

The soil surveys that comprise your AOI were mapped at 1:24,000.

Warning: Soil Map may not be valid at this scale.

Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale.

Please rely on the bar scale on each map sheet for map measurements.

Source of Map: Natural Resources Conservation Service Web Soil Survey URL: http://websoilsurvey.nrcs.usda.gov Coordinate System: Web Mercator (EPSG:3857)

Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required.

This product is generated from the USDA-NRCS certified data as of the version date(s) listed below.

Soil Survey Area: Island of Hawaii Area, Hawaii Survey Area Data: Version 7, Sep 25, 2014

Soil map units are labeled (as space allows) for map scales 1:50,000 or larger.

Date(s) aerial images were photographed: Data not available.

The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident.

Soil Map—Island of Hawaii Area, Hawaii (Hilea_Soil Report)

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

11/13/2014

Map Unit Legend

Island of Hawaii Area, Hawaii (HI801)

Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI

10 Lava flows, ̀ a`a, 2 to 20 percent slopes

153.8 50.8%

272 Kanohina ashy very fine sandy loam, 2 to 10 percent slopes

0.6 0.2%

541 Lava flows-Puueo complex, 2 to 20 percent slopes

6.9 2.3%

734 Kanohina-Lava flows complex, 2 to 10 percent slopes

141.4 46.7%

Totals for Area of Interest 302.7 100.0%

Soil Map—Island of Hawaii Area, Hawaii Hilea_Soil Report

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

AASHTO Group Classification (Surface)—Island of Hawaii Area, Hawaii

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

11/13/2014

233700 233900 234100 234300 234500 234700 234900

233700 233900 234100 234300 234500 234700 234900

19° 7' 58'' N

5°

1'

4' ' W

19° 7' 58'' N

5°

1'

1'

' W

19° 7' 4'' N

5°

1'

4'

' W

19° 7' 4'' N

5°

1'

1'

' W

N

Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 5N WGS84 0 350 700 1400 2100

Feet 0 100 200 400 600

Area of Interest (AOI)

Soils Soil Rating Polygons

A-1

A-1-a

A-1-b

A-2

A-2-4

A-2-5

A-2-6

A-2-7

A-3

A-4

A-5

A-6

A-7

A-7-5

A-7-6

A-8

Not rated or not available

Soil Rating Lines A-1

A-1-a

A-1-b

A-2

A-2-4

A-2-5

A-2-6

A-2-7

A-3

A-4

A-5

A-6

A-7

A-7-5

A-7-6

A-8

Not rated or not available

Soil Rating Points A-1

A-1-a

A-1-b

A-2

A-2-4

A-2-5

A-2-6

A-2-7

A-3

A-4

A-5

A-6

A-7

A-7-5

A-7-6

A-8

Not rated or not available

Water Features Streams and Canals

Transportation Rails

Interstate Highways

US Routes

Major Roads

Local Roads

Background Aerial Photography

The soil surveys that comprise your AOI were mapped at 1:24,000.

Warning: Soil Map may not be valid at this scale.

Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale.

Please rely on the bar scale on each map sheet for map measurements.

Source of Map: Natural Resources Conservation Service Web Soil Survey URL: http://websoilsurvey.nrcs.usda.gov Coordinate System: Web Mercator (EPSG:3857)

Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required.

This product is generated from the USDA-NRCS certified data as of the version date(s) listed below.

Soil Survey Area: Island of Hawaii Area, Hawaii Survey Area Data: Version 7, Sep 25, 2014

Soil map units are labeled (as space allows) for map scales 1:50,000 or larger.

Date(s) aerial images were photographed: Data not available.

The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident.

AASHTO Group Classification (Surface)—Island of Hawaii Area, Hawaii (Hilea_Soil Report)

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

AASHTO Group Classification (Surface)

AASHTO Group Classification (Surface)— Summary by Map Unit — Island of Hawaii Area, Hawaii (HI801)

Map unit symbol Map unit name Rating Acres in AOI Percent of AOI

10 Lava flows, `a`a, 2 to 20 percent slopes

A-1-a 153.8 50.8%

272 Kanohina ashy very fine sandy loam, 2 to 10 percent slopes

A-4 0.6 0.2%

541 Lava flows-Puueo complex, 2 to 20 percent slopes

A-1-a 6.9 2.3%

734 Kanohina-Lava flows complex, 2 to 10 percent slopes

A-4 141.4 46.7%

Totals for Area of Interest 302.7 100.0%

Description

AASHTO group classification is a system that classifies soils specifically for geotechnical engineering purposes that are related to highway and airfield construction. It is based on particle-size distribution and Atterberg limits, such as liquid limit and plasticity index. This classification system is covered in AASHTO Standard No. M 145-82. The classification is based on that portion of the soil that is smaller than 3 inches in diameter.

The AASHTO classification system has two general classifications: (i) granular materials having 35 percent or less, by weight, particles smaller than 0.074 mm in diameter and (ii) silt-clay materials having more than 35 percent, by weight, particles smaller than 0.074 mm in diameter. These two divisions are further subdivided into seven main group classifications, plus eight subgroups, for a total of fifteen for mineral soils. Another class for organic soils is used.

For each soil horizon in the database one or more AASHTO Group Classifications may be listed. One is marked as the representative or most commonly occurring.

The representative classification is shown here for the surface layer of the soil.

Rating Options

Aggregation Method: Dominant Condition

Component Percent Cutoff: None Specified

Tie-break Rule: Lower

Layer Options (Horizon Aggregation Method): Surface Layer (Not applicable)

AASHTO Group Classification (Surface)—Island of Hawaii Area, Hawaii Hilea_Soil Report

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

Hydrologic Soil Group—Island of Hawaii Area, Hawaii

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

11/13/2014

233700 233900 234100 234300 234500 234700 234900

233700 233900 234100 234300 234500 234700 234900

19° 7' 58'' N

5°

1'

4' ' W

19° 7' 58'' N

5°

1'

1'

' W

19° 7' 4'' N

5°

1'

4'

' W

19° 7' 4'' N

5°

1'

1'

' W

N

Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 5N WGS84 0 350 700 1400 2100

Feet 0 100 200 400 600

Area of Interest (AOI)

Soils Soil Rating Polygons

A

A/D

B

B/D

C

C/D

D

Not rated or not available

Soil Rating Lines A

A/D

B

B/D

C

C/D

D

Not rated or not available

Soil Rating Points A

A/D

B

B/D

C

C/D

D

Not rated or not available

Water Features Streams and Canals

Transportation Rails

Interstate Highways

US Routes

Major Roads

Local Roads

Background Aerial Photography

The soil surveys that comprise your AOI were mapped at 1:24,000.

Warning: Soil Map may not be valid at this scale.

Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale.

Please rely on the bar scale on each map sheet for map measurements.

Source of Map: Natural Resources Conservation Service Web Soil Survey URL: http://websoilsurvey.nrcs.usda.gov Coordinate System: Web Mercator (EPSG:3857)

Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required.

This product is generated from the USDA-NRCS certified data as of the version date(s) listed below.

Soil Survey Area: Island of Hawaii Area, Hawaii Survey Area Data: Version 7, Sep 25, 2014

Soil map units are labeled (as space allows) for map scales 1:50,000 or larger.

Date(s) aerial images were photographed: Data not available.

The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident.

Hydrologic Soil Group—Island of Hawaii Area, Hawaii (Hilea_Soil Report)

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

Hydrologic Soil Group

Hydrologic Soil Group— Summary by Map Unit — Island of Hawaii Area, Hawaii (HI801)

Map unit symbol Map unit name Rating Acres in AOI Percent of AOI

10 Lava flows, `a`a, 2 to 20 percent slopes

153.8 50.8%

272 Kanohina ashy very fine sandy loam, 2 to 10 percent slopes

D 0.6 0.2%

541 Lava flows-Puueo complex, 2 to 20 percent slopes

6.9 2.3%

734 Kanohina-Lava flows complex, 2 to 10 percent slopes

D 141.4 46.7%

Totals for Area of Interest 302.7 100.0%

Hydrologic Soil Group—Island of Hawaii Area, Hawaii Hilea_Soil Report

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

Description

Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms.

The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (A/D, B/D, and C/D). The groups are defined as follows:

Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission.

Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission.

Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission.

Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material.

These soils have a very slow rate of water transmission.

If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes.

Rating Options

Aggregation Method: Dominant Condition

Component Percent Cutoff: None Specified

Tie-break Rule: Higher

Hydrologic Soil Group—Island of Hawaii Area, Hawaii Hilea_Soil Report

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

Rainfall Data www.nws.noaa.gov

Home Site Map News Organization Search NWS All NOAA Go

General Info

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Precipitation Frequency (PF)

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• PF in GIS Format

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PMP Documents

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DATA DESCRIPTION

Data type: precipitation depth Units: english Time series type: partial duration

SELECT LOCATION

1. Manually:

a) Enter location (decimal degrees, use "-" for S and W): latitude: 19.124681 longitude: -155.525922 submit

b) Select station (click here for a list of stations used in frequency analysis for HI): select station

2. Use map:

a) Select location (move crosshair or double click)

b) Click on station icon

( show stations on map)

Map bookmarks:

Project area Hawaii Maui, Molokai, Lanai, Kahoolawe Oahu Kauai, Niihau

LOCATION INFORMATION:

Name: Pahala, Hawaii, US*

Latitude: 19.1247°

Longitude: -155.5259°

Elevation: 143 ft*

* source: Google Maps

PF tabular PF graphical Supplementary information

PDS-based precipitation frequency estimates with 90% confidence intervals (in inches)1

Duration Average recurrence interval (years)

1 2 5 10 25 50 100 200 500 1000

5-min 0.352 (0.313-0.409)

0.460 (0.392-0.552)

0.601 (0.511-0.724)

0.704 (0.595-0.853)

0.835 (0.698-1.02)

0.931 (0.770-1.15)

1.03 (0.837-1.28)

1.11 (0.899-1.42)

1.23 (0.969-1.60)

1.32 (1.02-1.74)

10-min 0.522 (0.464-0.606)

0.682 (0.582-0.819)

0.891 (0.757-1.07)

1.04 (0.882-1.27)

1.24 (1.04-1.51)

1.38 (1.14-1.71)

1.52 (1.24-1.90)

1.65 (1.33-2.10)

1.82 (1.44-2.37)

1.95 (1.51-2.58)

15-min 0.656 (0.582-0.761)

0.857 (0.731-1.03)

1.12 (0.951-1.35)

1.31 (1.11-1.59)

1.56 (1.30-1.90)

1.73 (1.43-2.14)

1.91 (1.56-2.38)

2.08 (1.67-2.64)

2.29 (1.81-2.97)

2.45 (1.89-3.24)

30-min 0.923 (0.819-1.07)

1.21 (1.03-1.45)

1.58 (1.34-1.90)

1.85 (1.56-2.24)

2.19 (1.83-2.67)

2.44 (2.02-3.01)

2.69 (2.19-3.35)

2.92 (2.36-3.71)

3.22 (2.54-4.18)

3.45 (2.66-4.55)

60-min 1.22 (1.08-1.41)

1.59 (1.35-1.90)

2.